ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Severe Combined Immunodeficiency (SCID)

Updated on May 28, 2019


Severe Combined Immunodeficiency Disease (SCID) represents numerous inherited genetic diseases. The basic clinical symptoms are quite similar in many forms of SCID where the affected individuals exhibiting defective T- and B-cell function. SCID can be subdivided according to the presence or absence of T-cells, B-cells and NK cells. SCID is more common in male individuals. The most common form of SCID is X-linked SCID, which accounts for almost half the cases of SCID. The affected persons have decreased number of B-cells and T-cells in the the body. Again, sometimes the numbers may be normal but the cells may be inactive, meaning that they can function properly. SCID can lead to many other severe diseases like cancer due to the inactivity of immune system.

Pic: Picture showing the difference between a normal human and a diseased human
Pic: Picture showing the difference between a normal human and a diseased human | Source

Clinical presentation of SCID

The signs and symptoms of SCID can be detected usually in a few months of birth of the affected individual. The symptoms include:

1. Viral infections: Cytomegalovirus (CMV), adenovirus, herpes simplex virus, rota virus etc. infections are commonly found in the SCID patients.

2. Crytosporidial infections

3. Candida albicans infections

4. Bacterial infections by S. aureus, P. jiroveci etc.

5. Aspergillus infections

6. Protozoan infections

7. Abnormality in Cell mediated immunity

8. Antibody deficiency

9. Chronic diarrhea

10. Skin rashes

11. Sinopulmonary infections

12. Sepsis

13. Oral and genital ulcers

14. Behavior problems and a decreased IQ

15. LIver infection

16. Meningitis

17. Poor wound healing

18. Frequent episodes of diarrhea, pneumonia, otitis and sepsis.

Since SCID is associated with defection in immune system, so any type of infections can occur because the immune system of that particular individual is weak. Viral, bacterial, fungal infections are common and many other diseases can also occur frequently.

Causes of SCID

1. X-linked SCID is caused by abnormalities in the gamma-c family of cytokines.

2. SCID associated with T-cell defects is caused by the abnormality in the T-cell receptor or CD3 deficiency.

3. SCID associated with enzyme deficiencies is caused by any defect in the adenosine deaminase gene or nucleoside phosphorylase gene.

4. SCID associated with defective HLAb expression is caused by any defect in the gene that express HLA class-II molecules.

In all the cases, the final result is that, the B-cell, T-cell and/or the NK cells will be defected in the diseases individual, resulting in defective immune system.

Genetic Basis of SCID

Pic: Picture showing various genes responsible for SCID.
Pic: Picture showing various genes responsible for SCID. | Source

Genetic Basis of SCID (cont.)

Various genes are responsible for SCID. IL7R gene, IL7R-alpha chain gene, CD45 gene, IL2RG gene, RAG1 & RAG2 genes, ARTEMIS gene, ADA gene etc. are genes that are responsible for SCID. Any defect in any one of these can cause SCID.

Again, defective JAK-STAT pathway also causes SCID.

Mechanisms of How SCID Occurs

There four mechanisms by which SCID occurs.

1. Premature cell death caused by the accumulation of purine metabolites. This phenomena occurs in adenosine deaminase (ADA) deficiency and due to this reason all the lymphocytes are equally affected. ADA deficiency accounts for about 15% of SCID cases.

2. Defective cytokine signaling can lead to SCID. These signals maintains the survival of T-cells and NK cells. Various cytokines, for example: IL-2, IL-4, IL-7 etc. are responsible for this phenomena. This type of SCID is the most frequent, with around 55% of SCID cases.

3. SCID can be caused by defections in the V(D)J gene rearrangement of T-cell receptors and B-cell receptors.

4. Defective pre-TCR and TCR signaling can also lead to SCID.

Pic: Proportions of SCID genotypes diagnosed with or without newborn screening.
Pic: Proportions of SCID genotypes diagnosed with or without newborn screening. | Source

Diagnosis of SCID

The suspected patient requires evaluation of both humoral and cellular immunity. Flow cytometric immunophenotyping of lymphocyte subsets in peripheral blood is important in patients suspected of having SCID. Again, evaluation of the number of active/naive T-cell in the peripheral blood can be done as a diagnostic procedure, since all types of SCID are characterized by a severe deficiency in naive T-cells. Moreover, the evaluation of humoral immunity may include measurement of Ig levels.

Treatment of SCID

1. Enzyme replacement therapy: In enzyme replacement therapy, ADA enzyme coupled to polyethylene glycol, is injected intramuscularly. These injections should be given once a week for the entire lifetime of the affected individual. This therapy gives the patient with ADA deficiency a better life to lead.

2. Stem cell transplantation: Stem cells are the cells that are collected from the blastula and these cells have the capability of converting to any cell type of the body. In stem cell transplantation, the stem cells are collected from the blastula, genetically engineered in vitro and transplanted into the patients so that the cells may convert into the B-cells, T-cell and NK cells.

3. Gene therapy: In gene therapy, the cells or bone marrow cells are collected from the patient, genetically engineered the cell in vitro so that the cells may express the desired gene that encodes immunologically important molecules, then the cells are transferred back to the patient. This strategy is effective if the pateint lacks any specific gene that is involved with the immunology.

Pic: Gene therapy to treat SCID
Pic: Gene therapy to treat SCID | Source

© 2019 Bishajit Sarkar


This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

Show Details
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
ClickscoThis is a data management platform studying reader behavior (Privacy Policy)